Table 824 Pesticide Removal Orientation

Removal Method

Adsorption onto clay and precipitates

Controlled self-destruction Degradation by biological systems

Chemical oxidation Activated carbon adsorption Membrane separation Incineration

Applicability

Soils and clay-bearing watercourses Water treatment coagulation processes Soil and watercourses Soil at point of pesticide application Watercourses receiving runoff containing pesticides Waste treatment system at pesticide handling facility Water and wastewater treatment systems

Water and wastewater treatment systems

Water and wastewater treatment systems

Concentrated residue disposal centration of carbon-14 in the fish over the concentration in water. The DDE metabolite of DDT was largely responsible for the undesirable accumulations in animal tissue noted.

In studies with tritium-labeled methoxychlor, accumulations of the pure compound and its degradation products in fish were of the order of 0.01 those for DDT (Metcalf, Sangha and Kapoor 1971). The presence of several degradation products and the relatively low accumu-

FIG. 8.2.11 Chemical structures of key pesticides. A. Chlordane; B. 2,4-D; C. DDT; D. Dieldrin; E. DNOCHP: F. DNOSBP; G. Endrin; H. Heptachlor; I. Lindane; J. Parathion; K. Sevin; L. Silvex; M. 2,4,5-T; N. Toxaphene.

lations in most organisms revealed the environmentally degradable nature of methoxychlor.

The organophosphate insecticides were less persistent in the aquatic environment than were the organochloride compounds (Graetz, et al. 1970). Depending on environmental conditions, degradation is by chemical or microbiological means, or both. Chemical degradation involves hydrolysis of the ester linkages. Hydrolysis can be either acid-catalyzed, e.g., ciodrin, or base-catalyzed, e.g., malathion. Microbial degradation can be by hydrolysis or oxidation. Partial degradation is often the case, although for diazinon, chemical hydrolysis of the thiophosphate linkage attached to the heterocyclic ring results in 2-iso-propyl-4-methyl-6-hydroxypyrimidine, which is degraded rapidly by soil microorganisms. Among the orthophosphates, parathion is one of the most resistant to chemical hydrolysis, but microbial degradation to aminoparathion can proceed.

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